Conventional aircraft environmental control systems incorporate an air cycle machine (ACM) for cooling and dehumidifying air supplied to an aircraft cabin. ACMs include a compressor section to compress air. The compressed air is discharged to a downstream heat exchanger and routed to a turbine. The turbine extracts energy from the expanded air to drive the compressor. The air output from the turbine is generally utilized as an air supply for a vehicle, such as the cabin of an aircraft. ACMs can be used to achieve a desired pressure, temperature, and humidity in the air that is transferred to the environmental control system of the aircraft.
ACMs often have a three-wheel or four-wheel configuration. In a three-wheel ACM, a turbine drives both a compressor and a fan which rotate on a common shaft. In a four-wheel ACM, two turbine sections drive a compressor and a fan on a common shaft. In either configuration, a first airflow can be directed into the compressor section and a second airflow can be directed into the fan section. After the first airflow is compressed by the compressor, the first airflow can be directed to a heat exchanger to cool the first airflow to a desired temperature before the first airflow travels to the turbine or turbines. The second airflow is directed by the fan section towards the heat exchanger to cool the first airflow.
The fan section includes a row of fan blades that rotate to draw the second airflow into the fan section and onto the heat exchanger. Fan blade breakage is one of the primary failure modes of the fan. In the event that one of the fan blades of the fan section should break free of the common shaft during operation, the severed fan blade could impact and damage the housing of the fan section. In traditional ACMs, the housing surrounding the fan section is often integral with the housing of the compressor section, forming a single component with a complex geometry that is expensive to repair or replace. When installing a new fan and compressor housing, improper alignment with mating components can cause decreased system performance.